1. Field of the Invention
The present invention relates to a chemical procedure to leach concentrates, mainly copper concentrates, consisting of blending the concentrate and the reagents to form a paste having gel characteristics. The equipment for the process is not that traditionally used to leaching concentrates.
2. Description of the State of the Art
There is strong motivation to develop metallurgic processes to replace the traditional, well established copper smelting and conversion which involve the serious disadvantage of generating a significant amount of contaminants, whose treatment or disposition is highly expensive since the environmental regulations are increasingly stringent.
For this reason, both copper producing countries and those processing flotation concentrates to obtain pure copper are rapidly looking for processes to replace the existing ones. Because of the higher costs involved in the disposition of the wastes generated, the current processes could become non-feasible, and current pyrometallurgical facilities could become obsolete.
The obvious alternatives which deserve worldwide attention are the processes following the aqueous approach to obtain the metal, which is denominated leaching. Originally, the aqueous approach, or hydrometallurgical processes, were not developed as an alternative to the pyrometallurgical processes. Their initial purpose was for treating the copper oxidized ores, which were not desirable for the smelting plants, due to their negligible amount of copper. On the other hand, there are hydrometallurgical industrial procedures both for treating low, and very low grade copper oxidized ores, and for copper sulfurated ores.
The interest in applying hydrometallurgical processes for treating copper concentrates begins in the sixties and the seventies of the 20th century. At the beginning of the seventies, the Bureau of Mines in the United States was the first one to try to develop a process to be industrially applicable for this purpose. Initially as an idea aimed at recovering the sulfur contents in the sulfides in a way different to the gaseous SO2, as in the case of smelting. This process was based on a leaching in chloride media. On the other hand, leaching copper ores (and silver) in chloride media was originally patented at the end of 19th century in U.S. Pat. No. 507,130 (1893). The process patented at that occasion, provided some issues had been solved, could have perfectly been applied to the copper concentrate leaching. After 100 years of development, along which a large amount of time and resources have been consumed, and a huge amount of scientific devices and patents have been generated, some of them have reached the industrial application level for some time, and are still fully present, tested at pilot, or semi-commercial scale, and only sixteen in commercialization stage. All these processes are likely to be equally profitable under the specific circumstances in which they are applied, and none of them is thought to be a universal panacea. It is believed that most of them will be industrially applied in the future, depending on the peculiar conditions of the place where they will be used. The process according to the present invention is a new, alternative process that could be the most advantageous one if some specific requirements are met.
The currently effective processes as mentioned above can be first divided according to the anion prevailing in the leaching solutions, that is: (a) systems in sulfate media, (b) systems in chloride-sulfate media, and (c) systems in chloride media, or in a more general form: halide systems.
According to this classification, the processes using the bacterial leaching (which are two) would fall in the category of sulfate systems, at least for now, since the future probability using bacteria bearing high chlorine concentrations (such as the halo-tolerant bacteria, according to “Importance of Microbiology in the Development of Sustainable Technologies for Mineral Processing and Wastewater Treatment) and could have certain advantages over those currently known, has not been determined to be invalid.
Next, the processes currently effective can be performed either at high pressure and high temperature, or at ambient pressure and temperature. The high pressure and temperature processes, which also were developed from the 1970's and thereafter, are the most common ones. A further division may be applied if the processes include a subsequent grinding of the concentrates to take them to a size passing 20 to 25 μm, or if they are kept at the original grain size distribution of the concentration stage.
Finally, a last condition is whether the system does or does not use some additive to improve the leaching performance.
All these processes are characterized for being performed in an agitated reactor, specially manufactured for this operation, where the manufacturing material should be resistant to the existing conditions, in terms of pressure, temperature, and chemical activity. All these processes are also characterized for being performed in a liquid, aqueous media, that is, a particle suspension containing certain proportion of solids, that is, concentrates in process. The amount of solids in the blend with the aqueous solution is commonly given in terms of solid weight percentage or pulp density, and the typical values range from 5 and 30%. The highest value found for the processes described above is 67% in weight, as stated in U.S. Pat. No. 4,144,310; that is, a similar value to that used in the concentrates hydraulics transportation, or concentrate-ducts, with relatively high terrain slopes. In all the processes known, the solids concentrations are lower than 67%. The key characteristic of these systems is that each particle of the concentrate is isolated, and reacts individually during the leaching process.
Another important characteristic is that in all these processes, the final oxidant is the oxygen, which may be injected as air or pure oxygen into the aqueous mixture in the reactor, or by filling the atmosphere contained over the aqueous solutions, as in the case of the pressure reactors.
In general, even though the oxygen of the air is the final oxidizer, it is not that the oxygen is the reagent directly participating in the reactions. Generally, the oxidation reactions take place through an intermediate oxidant, working as an oxidation-reduction couple, where the last electron acceptor is the gaseous oxygen. These oxidation-reduction couples can be, for example: Fe+3/Fe+2, Cu+2/Cu+ and NO2/NO.
This invention refers to an intrinsically chemical method, that is, non-biochemical, and in a sulfate-chloride ambient, and what is most innovative, that it is performed by means of equipment which is not typical to the copper concentrate leaching in reactors.
Unlike those above, the invention described below refers to a new process to leach concentrates, which is characterized by forming a paste between the concentrate and the reagents, a gel-like material having a high concentration of reagents provoking a reaction with sulfides, and that is left settling long enough for the dissolution reactions to be completed. This procedure does not require high pressures, or high temperatures, and obviously no type of bacteria. All the reactions take place naturally once the gel has formed, whose purpose is treating any kinds of copper concentrate, via hydrometallurgy, as shown below.